Grinding process and unit, and corresponding production process of a hydraulic binder

1. A grinding process of a raw material in a grinding unit, said unit including a first shop comprising a first mill and a first separator, an outlet from the first mill being connected to an inlet of the first separator, a second shop comprising a second separator and a second mill, an outlet from the second separator being connected to an inlet of the second mill, the second separator being fed by the material coming from the first separator, said grinding process comprising:

operating the first separator at a tangential speed of 15 to 25 m/s and a radial speed of 3.5 to 5 m/s; and

operating the second separator at a tangential speed of 20 to 50 m/s and a radial speed of 2.5 to 4 m/s.

2. The grinding process according to claim 1 , wherein

the first separator is operated at a tangential speed of 20 to 25 m/s and a radial speed of 3.5 to 4.5 m/s.

3. The grinding process according to claim 1 , wherein

the second separator is operated at a tangential speed of 25 to 45 m/s and a radial speed of 3 to 3.5 m/s.

4. The grinding process according to claim 1 , wherein the ratio between the tangential speed of the second separator and the tangential speed of the first separator is from 1.6 to 2.4.

5. The grinding process according to claim 4 , wherein the ratio between the tangential speed of the second separator and the tangential speed of the first separator is from 1.8 to 2.2.

6. The grinding process according to claim 1 , wherein the ratio between the radial speed of the first separator and the radial speed of the second separator is from 1.1 to 1.5.

7. The grinding process according to claim 6 , wherein the ratio between the radial speed of the first separator and the radial speed of the second separator is from 1.2 to 1.4.

8. The grinding process according to claim 1 , comprising:

a) grinding of the raw material to he ground in the first mill to provide a first ground material;

b) separating of the first ground material in the first separator to provide a first fine fraction and a first coarse fraction;

c) re-circulating the first coarse fraction towards the first mill;

d) separating the first fine fraction in the second separator to provide a second fine fraction and a second coarse fraction;

e) storing the second fine fraction in a storage means;

f) grinding the second coarse fraction in the second mill to provide a second ground material;

g) separating the second ground material in the second separator.

9. A process for production of a hydraulic binder comprising:

(i) grinding at least two materials with a grinding process according to claim 1 ;

(ii) mixing the materials obtained in step (i) with other optional ground or not ground materials.

10. The process according to claim 9 , wherein the grinding operation in step (i) is an operation during which the materials are ground separately.

11. A grinding unit for carrying out a grinding process of a raw material, said grinding unit comprising:

a first shop comprising a first mill and a first separator, an outlet from the first mill being connected to an inlet of the first separator;

a second shop comprising a second separator and a second mill, an outlet from the second separator being connected to an inlet of the second mill;

the second separator being fed by the material coming from the first separator, wherein the first separator is configured to operate at a tangential speed of 15 to 25 m/s and a radial speed of 3.5 to 5 m/s and the second separator is configured to operate at a tangential speed of 20 to 50 m/s and a radial speed of 2.5 to 4 m/s.

12. The grinding unit according to claim 11 , wherein the second mill is a ball mill comprising an enclosure of cylindrical shape having a length L, a diameter D and a L/D ratio less than or equal to 2.5, L and D being expressed in the same unit of measurement.

13. The grinding unit according to claim 11 , wherein the second shop comprises a compressive mill as second mill, and said second separator, an outlet of the separator being connected to an inlet of the compressive mill, the separator being fed with gas by:

a first inlet of gas located at the level of the compressive mill, the gas coming from the first inlet of gas first passing through the mill then through the separator;

a second inlet of gas located at the level of the separator, the gas coming from the second inlet of gas only passing through the separator and mixing with the gas from the first inlet of gas after its passage through the compressive mill.

14. A cement plant comprising a grinding unit according to claim 11 , connected to an inlet of a cement plant kiln.